The present invention relates to a method and a system for automatically performing a forward/reverse gear change without requiring the manual disengagement of the vehicle main clutch. The invention has particular application in agricultural tractors where eg frequent three point turns on field headlands and repeated backward and forward travel during loading work involve frequent forward/reverse gear changes.
The concept of a system for effecting a direction change by shifting a lever or button, etc, without touching the clutch pedal is known. The word "powershuttle" is often used to describe such a system.
Known powershuttles generally employ two clutches working against each other to control the transfer of power between gear trains that remain continually in mesh. That is to say, no synchromesh is employed and the shift is effected using a similar procedure to that employed in making a shift between two forward gears in a "power shift" transmission. Thus, one clutch is arranged to transmit or to disable a reverse direction drive to the vehicle's driving wheels, whilst the other is arranged to transmit or disable a forward direction drive.
The control of the forward and reverse clutches will generally be electronic, taking into account speed, engine revs, and possibly other factors to set an optimum rate for the respective clutches to engage and disengage.
This type of system obviously requires a reverse direction clutch in addition to its main clutch.
The problem with such a powershuttle is that a great deal of energy needs to be dissipated by the clutches during a gear change, and the additional reverse clutch therefore needs to be substantial. This makes for high cost and the requirement for room under the bonnet to house the extra clutch.
The object of the present invention is to alleviate the above problems and provide a powershuttle system which is relatively inexpensive and requires no more room under the bonnet than is taken up by an equivalent transmission with a manual forward/reverse change.
A further object of the invention is to provide a powershuttle system that is readily installed in a vehicle with a conventional manual forward/reverse gearshift facility, with the minimum of adaptation; in particular, leaving the majority of the components in the transmission unaffected.